TWICE WITHIN two weeks, Bill Clinton has fulfilled one of the major duties of any American president: to see clearly a danger to American peace, at home or abroad, to speak in public candor about it, and to start acting to meet it.

And twice Clinton has found himself denounced by important segments of the American society that is the target of the terrorist danger he sees. In politics and journalism, the president's call to Americans to speak out against armed bigotry is being widely and deliberately twisted and distorted. In business, the automatic reactions to his decision to impose a trade and investment embargo against Iran have been to call it useless or harmful.

When the next bomb is exploded in the next Oklahoma City, or when the U.S. has to decide whether Iran's nuclear plants have to be bombed before they produce weapons or after, these attacks against Clinton will no longer be important. But, as we wait, they serve as museum-quality specimens of how mean- spirited and suicidal American establishments can be when they really put their minds to it.

After Oklahoma, Clinton said in several speeches that those Americans who did not agree with fellow citizens who exercised their constitutional rights to spread paranoia at least should use their own right to speak against them. Platitudes -- but important ones, since so few Americans do stand to speak against hate warriors of right or left.

In one speech, Clinton spoke a few words about some hate-mongering coming by radio, another piece of important obviousness. They pounced -- the commentators, columnists and Democratic and Republican politicians who would not forgive Clinton if he said that the sun would rise tomorrow.

Some of the fury came from people who found that the shoe fit. But what was startling, and rather disgusting, were the charges, repeated endlessly in the mainstream press and TV, that by daring to mention radio, the president was scapegoating and trying to stifle criticism of the government.

In politics, members of both parties clucked at Clinton and assured us that the country would not be taken over by extremist nuts. As for business, it generally takes the attitude that the U.S. can use the lever of economic power only when it is in its business interests to do so.

The business reaction to the Iran embargo was perfect knee-jerk: It will do no good because Iran will sell its oil elsewhere when American firms stop buying their current share of about 30 percent. The truth is the embargo is of major importance. It weakens foreign confidence in Iran as an investment market and strengthens the domestic opponents of the increasingly unpopular regime.

Used properly by Washington, it will be notice to our allies that they can expect U.S. economic pressure to back off from trading with a terrorist, nuclear- bent Iran. Representative Peter King, R- N.Y., says he will ask Congress to add a boycott of foreign companies that do business with Iran. That should focus our allies' attention on whether they prefer to do business with Iran or America.

Most important to American ethics, the embargo will end the contribution of American capitalism to Iran's drive to become a military nuclear power within 5 to 10 years, with Russian and Chinese help. So the embargo should strengthen Clinton when he delivers the critical message to Yeltsin: The Russian decision to build a nuclear plant for Iran is a danger that the U.S. cannot tolerate.

The Clinton people naturally do not wish to push Yeltsin to the advantage of his Russian enemies. But that is not as great a danger as allowing Russia to sell Iran the power of nuclear blackmail or nuclear terrorism.

Clinton has started the work of engaging with domestic and foreign terrorism, with allies abroad or without them. That reality is much more important than the distorting mirrors being held up to that work, so cynically, so destructively.